Many modern ignition distributors for use with internal combustion engines provide contactless signaling transducer elements or generators constructed, for example, in the form of induction generators or magnetic elements using a Hall semiconductor device. The outputs from these transducers are used as control signals for the ignition sparks. The exact adjustment of ignition sparking can be carried out electronically or, very simply, mechanically by using a vacuum diaphragm chamber to provide ignition timing adjustment in dependence on loading on the engine, and a centrifugal adjustment element which changes the ignition timing, independently of loading, based on speed of the engine. The centrifugal adjustment device can be located within the distributor-pulse generator combination.
If the ignition timing is not in accordance with design requirements, and particularly if the ignition timing is too advanced, the engine may be subjected to knocking or pinging. Knocking or pinging is caused by pulse waves occurring upon combustion of the fuel-air mixture which can be heard as oscillations of the engine at audible frequencies. Pinging or knocking should be avoided since it places heavy thermal loading on the inner walls of the combustion chamber of the cylinder and the adjacent surfaces of the piston, which may lead to degradation of the surfaces, removal of material therefrom, and otherwise, particularly upon extended occurrence of pinging, to damage of the engine.
It is desired to operate the engine as close as possible to its maximum power design output level and, thus, to operate the engine just below the characteristic timing of the ignition at which pinging or knocking might result. Of course, by detuning the timing, that is, by always retarding the timing beyond the optimum setting, pinging or knocking can be avoided. To obtain maximum power output, however, it is desirable to so operate the engine that it is just below the knocking limit and, hence, it is necessary to rapidly and reliably determine knocking or tendency to destructive knocking of the engine.
Sensing knocking, so that the continuous operation under knocking condition can be avoided, requires suitable transducers. The transducers must provide output signals of such characteristics that knocking oscillations occurring in the IC engine can be reliably distinguished from noise or other disturbance background signals. Accordingly, it has been proposed to measure signals for knocking recognition only during a strobing interval, that is, during a measuring window or measuring time interval which is so arranged that it falls within a predetermined angular range of position of the crankshaft, so that the particular position of the piston within the cylinder, which is determined by the angular position of the crankshaft, can be associated with the strobing interval or the measuring window. It has been proposed to determine the strobing interval or the measuring window by deriving a signal from the ignition control signals. It has been found that this has the disadvantage that the ignition signal does not always occur synchronously with respect to a predetermined angular position of the crankshaft, due to the aforementioned adjustment for speed and loading of the engine.